1. Field of the Invention
The present invention relates to an image forming apparatus for forming an image on a record medium, which includes a particle detecting device to detect particles by irradiating a light beam to particles existing in a gas, liquid or transparent solid and by detecting a scattered light.
2. Description of the Related Art
Hitherto, a device which irradiates a light such as a laser beam to particles and detects the particles by detecting a scattered light thereof has been developed. As particles of detection objects, there are various particles including a solid particle, a microorganism and a molecular aggregate.
Besides, in recent years, an image forming apparatus such as a copier becomes precise, and in order to perform excellent image formation, when the amount of minute paper powder in the image forming apparatus becomes a specific amount or more, it becomes necessary to remove the powder. Thus, the development of a particle detecting device to detect the minute paper powder in the image forming apparatus has been demanded.
In the related art, there is proposed a technique in which a laser beam is reciprocated so that particle detection accuracy is raised (for example, International Publication No. WO2004/025279).
This is such that a reflecting film is provided on a nonlinear optical crystal through which a light beam is transmitted, a reflecting mirror is provided in a light path of the light beam whose wavelength is converted, and the light beam whose wavelength is converted is reciprocated between the reflecting film and the reflecting mirror, so that a light with higher energy density than a light irradiated from a light source can be obtained.
However, in this technique, since the light beam to be irradiated to the particles is one straight line, the range where the light can be irradiated is limited. Further, the number of particles to which the light beam is irradiated is not increased as compared with the case where the light beam is not reciprocated. Accordingly, there is a problem that this is not effective in the object of detecting the presence or absence of particles existing in an area to be observed or the number thereof with high accuracy.